Liquid level gauges of the type having a buoyant float mounted on a pivoting float arm which responds to changes in the liquid level being measured are well known. Such pivoting float-type gauges typically utilize mechanical or electrical mechanisms that sense the angular position of the float arm with respect to a stationary support arm or other structure. The mechanism then provides an external indication of the corresponding liquid level. Since the liquid level indication is based on a measurement of the angle between the float arm and another structure, it is important that the float arm have a known configuration in the plane of pivoting motion in order to preserve the accuracy, precision and calibration of the gauge.
The measurement range of a typical pivoting float-type gauge depends (in part) upon the range of vertical positions which can be reached by the float's arc of motion (any liquid level above or below the float's range of travel being unmeasurable). It is therefore often desirable to make the float arm as long as possible consistent with providing sufficient clearance for the float to pivot.
In some applications, for example, on pressurized tanks used for storing liquids such as liquefied petroleum gas (often referred to generally as "LPG"), the liquid level gauge is provided with a threaded gauge head for mounting into a threaded pressure fitting on the tank. In such cases, the float, float arm, support arm and other in-tank components of the gauge are inserted through a passage in the threaded fitting on the tank. The entire gauge is then rotated to cause the threaded gauge head to engage the threaded fitting and form a pressure-type seal.
It is known that pivoting float-type gauges can be damaged during installation if the float or float arm strikes the interior walls of the tank or other stationary objects as the gauge is being screwed into the threaded tank fitting. Since the float arm typically hangs downward in an empty tank such damage is unlikely if the gauge is slowly screwed into the fitting by hand or using a manual wrench, as was common industry practice in the past. However, it has now been discovered that power wrenches are increasingly being used for installing screw-in float type gauges into tanks. Power wrenches typically spin the gauge much faster and with more force during installation than a manual wrench. The centrifugal force that results from rapid spinning of a gauge during installation can cause the float and float arm to rapidly swing from a downward, generally vertical position to a laterally extending, generally horizontal position. In many cases, and especially where the storage tank is narrow and/or where the gauge is installed near the sidewall of the tank, the revolution of a horizontally oriented float arm about a vertical axis such as the support arm can result in the float or float arm striking the walls or other interior components of the tank. If the float arm strikes the interior of the storage tank (especially if it is being rotated by a power wrench), this can result in damage to the float, bending of the float arm, damage to the float arm pivot mechanism, twisting of the support arm, or other damage which can adversely affect the calibration, accuracy and/or precision of the gauge. A need therefore exists, for a pivoting float-type liquid level gauge having a float arm that will not be damaged if an obstacle is encountered in the interior of the tank during installation. A need further exists, for a pivoting float-type gauge having a mechanism which retains its accuracy and calibration if the float arm encounters an obstacle during installation.